It is estimated that up to 8% of children less than 3 years of age and 2% of adults are affected by food allergies (reviewed in 1). While food-induced allergic reactions are the most common cause of outpatient anaphylaxis,2 the majority of severe reactions of this kind are caused by peanuts and tree nuts. 3,4 Most plant food allergens can be found among pathogenesis-related proteins, seed storage albumins and globulins, and a-amylase and protease inhibitors.
A previous study by Teuber et al. 6 documented the cloning and sequencing of a gene encoding Jug r 1, a major allergen in the English walnut, Juglans regia. Jug r 1 is a 2S albumin seed storage protein and possesses important homologies in amino acid sequence with other 2S albumin proteins from Brazil nut, cottonseed, castor bean, and mustard.6 Like many 2S albumins, Jug r 1 is synthesized as a precursor protein and cleaved into a large and small subunit joined by disulfide bridges. It is currently believed that patients with life-threatening allergies to walnuts and other tree nuts will rarely become tolerant of these foods 7 and consequently face a lifetime of avoidance. 8 Avoidance, however, is often difficult due to the ubiquitous nature of these foods and the potential for cross-contamination during their processing. 7 
Many approaches to allergen immunotherapy under investigation today are based on a detailed knowledge of the amino acids found in IgE-reactive B-cell epitopes. 9, 10, 11, 12 These reactive sites can be either linear or conformational. Typically, a linear epitope contains a stretch of contiguous amino acids spanning 5-10 residues in the antigen, while residues distant in the primary sequence but proximate in the folded protein comprise a conformational epitope. 13 In recent years, the genes encoding several proteins with allergenicity, such as Jug r 1, have been cloned and expressed using molecular biology techniques. 6, 14, 15, 16 Despite the rapidly increasing number of recombinant allergens, relatively few IgE-reactive B-cell epitopes have been defined. 17-29 